(a) Field of the Invention
This invention relates to textile fabric treatment compositions for application to textile fabrics, which reduce electrostatic charge on said fabrics and which improve the "feel" thereof, and to a method of use of such compositions for such purpose.
(b) Information Disclosure Statement
It is known that textile fabrics prepared from fibers which have a high dielectric constant and a low electrical conductivity are highly susceptible to the development of an electrostatic charge on the fabrics particularly in a dry atmosphere. (See for example Whitehead U.S. Pat. No. 2,153,358.) The development of such electrostatic charge in garment fabrics causes the garments to display an undesirable tendency to cling to the wearer rather than to adopt a more natural and comfortable drape on the wearer's body. The problem of electrostatic charge build up on fabrics is particularly acute in dry weather, apparently because any inherent electrical conductivity the fabrics may possess, which would tend to dissipate static charge, is diminished considerably under such dry conditions. (See for example Dasher et al. U.S. Pat. No. 4,129,505.)
There have been several general approaches by the prior art to the solution of the problem. In one approach, attempts have been made to essentially permanently increase the electrical conductivity of spun fibers by incorporation of various ionic species either within the structure of the fibers or as a coating thereon during the spinning process. Thus in the above noted U.S. Pat. No. 2,153,358, the spun fibers, such as cellulose esters or ethers, are either coated with, or are spun so as to incorporate within the fibers, a variety of electrolytes. In Smith et al. U.S. Pat. No. 3,696,078, the problem is addressed by the incorporation within spun nylon fibers of certain phosphonium bromides in combination with certain polyalkoxylated agents. The method is said to have an advantage over previous methods in which polyalkoxylated agents are used to provide an antistatic effect, because the antistatic properties of spun fibers treated with the phosphonium bromide/polyalkoxylated agent combination are stable to subsequent rinsing or washing of the fabrics with which those agents are incorporated.
In another approach, a composition containing an antistatic agent is either formulated as part of a laundry detergent composition or is added as a separate composition to a laundry wash cycle. Thus Montgomery et al. U.S. Pat. No. 3,959,155 describes "fabric softener and antistatic compositions" for combination with a detergent, containing a "softening component comprising a smectite clay", an "antistatic component" comprising "a quaternary ammonium compound" and "an electrically conductive salt" of aluminum or lithium dispersed therein. Woodward U.S. Pat. No. 4,392,965 describes a fabric softener/antistatic composition containing a water insoluble quaternary ammonium salt, for example an N,N-dialkyl-N,N-di-lower-alkylammonium salt wherein the anion is derived from an organic carboxylic acid. The insoluble quaternary ammonium salts are said to be compatible with anionic laundry detergents and are intended to be added, as separate ingredients, to a laundry wash cycle.
Alternatively, and more conventionally, the antistatic agent is applied to laundered fabrics in a clothes dryer during the drying cycle. Thus Rudy U.S. Pat. No. 3,650,816 describes an additive for application to clothes in a dryer for imparting both fabric softening and antistatic properties to fabrics. The compositions are formulated as aerosol sprays which, when sprayed onto the drum of a laundry dryer, form a hard surfaced coat which is then uniformly transferred to the fabrics as they are tumbled over the drum surface during a drying cycle. Kardouche U.S. Pat. No. 4,237,155 describes fabric softener/antistatic compositions containing, as the softener/antistatic agent, a tertiary amine salt produced by the reaction of a tertiary amine with a carboxylic acid. The compositions may optionally contain cationic softener/antistatic agents, such as quaternary salts of the N,N-di-long chain-N,N-di-lower-alkylammonium type, such as an N,N-ditallow-N,N-dimethylammonium chloride (or methosulfate). The compositions are applied to fabrics during a drying cycle either from a sponge, from a paper impregnated with the composition or by spraying from an aerosol can into the dryer.
Other means of uniformly distributing fabric conditioners of various kinds over fabrics in a clothes dryer involve use of a so-called distributing agent, as illustrated by Rudy et al. U.S. Pat. No. 4,012,326 which describes a fabric softener composition containing a distributing agent, e.g., ammonium carbonate, which volatilizes at temperatures encountered in a dryer thus helping to spread the composition throughout the mass of the fabrics in the dryer. The Rudy et al. compositions are intended to be added to the clothes dryer at the beginning of a drying cycle while the clothing is still wet. The distributing agent used in the compositions therefore can also comprise a hydroxycarboxylic acid, such as citric, tartaric or gluconic acid, which is soluble in the water accompanying the wet wash. The acids, because of their acidity, promote the solubilization and spreading of cationic fabric softeners. The softeners so employed include, for example, N,N-distearyl-N,N-dimethylammonium chloride.
German Application No. 2,166,494 describes antistatic compositions for spray application in carpet shampoo, floor cleaning or domestic cleaning formulations, containing, as the effective antistatic agent, an ammonium, alkali metal or alkaline earth metal salt of carboxylic acids containing from two to eight carbon atoms which can contain a hydroxy group. Of the latter type of salt, sodium and ammonium glycolate are specifically mentioned as being effective. Salts of lactic acid, although within the ambit of the generic disclosure, are not specifically mentioned, but in any case as will be demonstrated hereinafter, we have found sodium lactate to be completely ineffective as an antistatic agent when applied as a spray to textile fabrics.
Still another approach to the problem of solving the static cling problem in wearing apparel involves application of an antistatic composition to the fabrics in an essentially anhydrous environment. Thus McLaughlin U.S. Pat. No. 3,806,359 describes a fabric softener composition which is dispensed as a foam from a pressurized aerosol container onto clothing in a dryer which is then subjected to tumbling in the dry heat of the dryer. Dasher et al. U.S. Pat. No. 4,129,505 describes an antistatic composition for direct application to dry clothing which comprises a quaternary ammonium fabric softener and ammonium acetate in ethanol in a pressurized aerosol formulation which is sprayed onto the clothing. The ammonium acetate is said to act in cooperation with the fabric softener, because the former is hygroscopic and deliquescent and thus picks up sufficent moisture from the atmosphere to help maintain the ionic character of the quaternary. The composition thereby increases the electrical conductivity of the fabrics to which it is applied thus lessening the static charge.
It is thus seen that, although quaternary ammonium salts, such as quaternaries of the N,N-di-long chain-N,N-di-lower-alkylquaternary ammonium type, have been known to function both as fabric softeners and as antistatic agents, the antistatic properties inherent in their ionic nature are generally lost, or at least ineffectively utilized, unless the fabric softener/antistatic agents are formulated or used in some particular way which fixes the agents either to or within the molecular framework of the fabric substrate with which they are associated; or unless means are adopted which help to more thoroughly spread the agents throughout the mass of the textile fabrics to which they are applied; or unless other ingredients are used to maintain an essentially permanently moist environment for the agents.
We have surprisingly found that, when quaternary ammonium salts of the N,N-dialkyl-N,N-di-lower-alkyl-ammonium type are formulated with certain relative amounts of a lactic acid salt, the formulations, when applied to fabrics, impart antistatic properties to the fabrics at concentrations at which the quaternary salts alone impart either significantly less effective antistatic properties or none at all. This enhanced antistatic effect of the combination of lactic acid salt and quaternary ammonium salt thus permits the use of the latter at concentrations significantly lower than otherwise possible while still maintaining antistatic effectiveness, a factor which not only has the advantage of reducing cost, but also of minimizing any undesired effects which the use of larger quantities of the quaternary ammonium salts may have on the treated fabrics, e.g. adverse changes in "feel" or "hand", or loss of absorbency or discoloration.
This finding is quite unexpected, because to our knowledge lactic acid salts have not been used to provide antistatic effects in textile fabrics and, in fact as stated above, experiments carried out by us with sodium lactate have established the latter salt per se to be completely ineffective as an antistatic agent when applied to textile fabrics in the form of a spray at concentrations at which they are employed in this invention, this notwithstanding the fact that salts of lactic acid are disclosed in the prior art to produce an antistatic effect on non-fibrous cellulosic plastic sheets which have been impregnated therewith (see Koch U.S. Pat. No. 3,447,948).